This invention relates to the art of civil engineering, and more particularly to reversible percussive action machines.
The machine according to the invention can be used for driving holes in the ground during trenchless laying of underground communications.
In addition, the proposed machine can be used as an impact producing unit for driving casings into the ground, sinking piles, and taking soil samples for civil engineering surveying and geological explorations.
An ever increasing use of reversible percussive action machines, particularly for making short-length blind holes to receive cast-in-place piles and for civil engineering and geological surveying, calls for a substantially higher reliability of such devices especially with respect to the reversal mechanism which, along with structural reliability, simplicity and small size, must be sufficiently responsive to, for example, a mere axial pull applied to a flexible hose connected to the machine. These demands account for a range of reversible percussive action machine constructions now being used with varying degree of success.
There is known a reversible percussive action machine (cf., e.g., USSR Inventor's Certificate No. 263,482, IPC E 02 F 5/18, published 1965) which comprises a housing accommodating a hammer capable of reciprocating under the action of a fluid under pressure, and a system for distributing the fliud under pressure to ensure that the hammer delivers impacts on either the front portion of the housing for the forward travel of the machine, or on the rear portion of the housing for the return travel of the machine.
The distribution of the working fluid under pressure in the two operating modes of the machine is controlled by a valving member movably connected to the hammer.
This valving member can be fixed relative to the housing in two positions, particularly front and rear positions; in its front position the valving member controls the distribution of the working fluid to ensure the forward travel of the machine, whereas in the rear position it redistributes the flow of fluid under pressure for the machine to travel backwards.
The valving member is connected to the housing through a tube element affixed to a flange. The flange is rigidly secured inside the housing. Locking of the valving member relative to the housing is done by means of a ball received by a laterally extending hole in the tube and alternately in one of grooves of the valving member in which this ball is held by a spring-loaded nipple having a bevel and a recess and passed through the tube and the interior of the flange. The working fluid under pressure is fed to the nipple by way of a flexible hose connected thereto. The valving member is further spring-loaded relative to the flange.
In order to switch the machine over to the reverse travel operation, it is necessary by applying a tension force to the flexible hose to move the nipple rearwards so that its recess would be opposite the ball. Under the action of a force exerted by the fluid under pressure on the front end face of the valving member the latter tends to move rearwards as far as it goes. Therewith, the ball is forced to the groove of the nipple, and subsequent to releasing the tension applied to the flexible hose it is moved by the nipple bevel to the front recess of the valving member to be locked in position relative to the tube, flange and housing. In this position of the valving member the hammer executes reciprocations inside the housing and delivers impacts on the rear portion thereof for the machine to travel back along the already made hole toward the hole mouth.
For resuming the forward percussive action of the machine it is necessary to terminate the supply of fluid under pressure and pull on the flexible hose. In consequence, the nipple moves rearwards so that the ball assumes a position opposite the nipple groove. The force of the spring of the valving member acts to move the ball to the nipple groove for the valving member to be displaced forward so that its rear recess is opposite the ball. After releasing the pull force on the flexible hose the nipple moves forward under the action of another spring to displace by its bevel the ball to the rear recess of the valving member and fix it in position relative to tube, flange and housing. With this position of the elements and after feeding the fluid under pressure to the machine the hammer resumes its reciprocations and delivers impacts on the front portion of the housing, whereby the machine travels forward.
However, the aforedescribed reversible percussive action machine is inherently unreliable due to possible inadvertent switchovers from the forward to reverse travel operation caused by insufficient urging of the ball by the spring-loaded nipple. It deems impossible to make ball urging more reliable, since it requires the use of a spring of greater force to spring-load the nipple. Accordingly, this spring force must not be greater than a tension force manually applied to the flexible hose connected to the nipple during switching machine operation from the forward to the reverse travel.
In addition, the above machine features a rather low reliability due to insufficient service life of its parts caused by high contact stressed in the ball and cooperating parts of the valving member, nipple and tube, since the ball is capable of only a point contact therewith.
The machine is further characterized by a relatively low specific power (power per unit area of machine crosssection), since the use of the ball entails an increase in machine diameter.
There is also known a reversible percussive action machine (cf., USSR Inventor's Certificate No. 1,118,747; IPC E 02 F 5/18, published 1980) comprising a housing accommodating a hammer reciprocating under the action of a working fluid under pressure and delivering impacts on the front portion of the housing during the forward travel and on the rear portion during the return travel of the machine, and a valving member for controlling the distribution of the working fluid under pressure movably connected to the hammer and provided with means for fixing it relative to the housing in two positions for the forward travel and the reverse travel of the machine, respectively.
The valving member is connected to the housing through a resilient plate secured on this member and a flange rigidly affixed to the housing. The resilient plate has a projection to cooperate with the flange, and a beveled lug to engage with a bevel of a sleeve provided at the other end thereof with a flexible hose for feeding the working fluid under pressure. The valving member further has a stop and is spring-loaded relative to the flange; whereas the flange has a groove to receive the lug of the resilient plate, the flange having a recess to receive the projection of the resilient plate.
When the machine operates n the forward travel percussive action mode, the lug of the flexible plate occupies the recess of the flange to lock the valving member in the frontmost position relative to the housing. Subsequent to feeding the working fluid under pressure the hammer reciprocates inside the housing and delivers impacts on the front portion thereof, whereby the machine moves forward in the ground leaving a hole behind.
In order to switch the machine over to the reverse percussive action mode of operation, it is necessary to pull on the flexible hose and thus move the sleeve rearwards. The sleeve bevel transmits a radial force to the beveled lug of the flexible plate. Under the action of this force the resilient plate is caused to enter the groove, and the projection of the flexible plate is brought out of engagement with the recess of the flange. The pressure of the working fluid makes the valving member move rearwards until the stop of the valving member is in engagement with the flange. In this position the valving member ensures reciprocations of the hammer in the housing of the machine accompanied by the delivery of impacts on the rear portion of the housing, whereby the machine moves along the hole backwards to the hole mouth, i.e., the percussive action of the machine is reversed.
For resuming the forward travel of the machine the supply of the working fluid under pressure is terminated. The spring loading the valving member relative to the flange acts to move the valving member to its front position corresponding to the forward percussive action of the machine (the lug of the flexible plate enters the recess of the flange and locks the valving member relative to the housing in the frontmost position), whereby subsequent to feeding the fluid under pressure the hammer resumes its reciprocations to deliver impacts on the front portion of the housing and the machine functions in the forward percussive action mode of operation.
One disadvantage of the aforedescribed machine is that it is not sufficiently reliable in operation, since arbitrary switchover from the forward to the reverse percussive action is possible by accidentally applying a pull force to the flexible hose.
In addition, low reliability may be caused by the possible damage of the resilient plate under the action of axial forces exerted thereon by the valving member and produced by the fluid under pressure in the working chambers of the machine. The resilient plate is also susceptible to damage due to the action of bending forces exerted thereon by the lug when it cooperates with the flange.